When imaging with the aid of tomographic imaging facilities, slice or volume images of the interior of an examination object are obtained. Examples of such tomographic imaging facilities are units for X-ray imaging, in particular computer tomographs and C-arc units, magnetic resonance tomographs, positron emission tomography (PET) units, SPECT (Single Photon Emission Computed Tomography) units or ultrasound tomography units.
Particularly, in the case of invasive medical operations, for his orientation the physician needs online image monitoring of the instruments introduced into the body such as, for example, catheters or biopsy needles. In this case, the tomography images must be displayed in good time, as far as possible. A short latency or delay time on the path between measured data acquisition and image display is therefore of particular importance in these applications.
Invasive operations are monitored by way of X-ray imaging in many instances. In order to reduce the radiation burden on the examining physician during the use of computer tomographs, it is known to switch off the radiation for a specific angular range during each revolution of the rotary frame (gantry) of the computer tomograph. A series of individual measurement scans result in this way.
A main image is reconstructed every complete revolution of the rotary frame from each of these measurement scans with the aid of a suitable algorithm, and subsequently displayed. However, this procedure lowers the image repetition rate considerably by comparison with a continuous measurement mode of the computer tomograph. In order to double this image repetition rate, up to now there has been inserted in each case between two temporally consecutive main images a synthetic intermediate image that is interpolated from the image data of these main images.
However, in this technique an intermediate image relating to two consecutive measurement scans n−1 and n can be calculated at the earliest when the current measurement scan n is terminated. The shortest possible latency time for displaying the main images is reached when the generation of the intermediate image is positioned at the end of the current measurement scan n. In order for all the images to appear at an interval of half a rotation of the rotary frame, however, in this case the display of the main image that is reconstructed from this measurement scan and is qualitatively of a substantially higher value must be artificially delayed by the time of half a rotation of the rotary frame.
Furthermore, the generation of the intermediate images by interpolation of the pixel intensity between two main images supplies adequate results only for scenes in which the image brightness of a location-varies over time such as, for example, in the case of bolus injections. However, when displaying images of scenes in which the location of an object changes over time, for example during biopsy, this type of interpolation supplies only a superposition of the initial and final positions of the object and not, as aimed at, the intermediate position.
WO 98/36690 A1 discloses a method for dynamic real-time image reconstruction in the case of which a starting image is firstly reconstructed from measured data of a complete measurement scan and is subsequently updated with additional measured data that originate from a subsequent partial scan at the respective slice position. The updating of the starting image is performed by adding an image matrix to the image just displayed. The added image matrix is obtained from a combination of the measured data additionally acquired by the partial scan with the measured data of the original measured scan, which correspond to the same scanning section.